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a cell in the basal layer of the epidermis that produces melanin under the control of the melanocyte-stimulating hormone

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/12/23 18:16:21」(JST)

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Melanocytes ⁱ/mɛˈlænɵsaɪt/ are melanin-producing cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea),^[1] the inner ear,^[2] meninges,^[3] bones,^[4] and heart.^[5] Melanin is the pigment primarily responsible for skin color.

Melanogenesis

Through a process called melanogenesis, these cells produce melanin, which is a pigment found in the skin, eyes, and hair. This melanogenesis leads to a long-lasting pigmentation, which is in contrast to the pigmentation that originates from oxidation of already-existing melanin.

There are both basal and activated levels of melanogenesis; in general, lighter-skinned people have low basal levels of melanogenesis. Exposure to UV-B radiation causes an increased melanogenesis. The purpose of the melanogenesis is to protect the hypodermis, the layer under the skin, from the UV-B light that can damage it (DNA photodamage). The color of the melanin is dark and it absorbs all the UV-B light and it blocks it from passing the skin layer.^[6]

Since the action spectrum of sunburn and melanogenesis are virtually identical, they are assumed to be induced by the same mechanism.^[7] The agreement of the action spectrum with the absorption spectrum of DNA points towards the formation of cyclobutane pyrimidine dimers (CPDs) - direct DNA damage.

Typically, between 1000 and 2000 melanocytes per square millimeter of skin are found. Melanocytes comprise from 5% to 10% of the cells in the basal layer of epidermis. Although their size can vary, melanocytes are typically 7 μm in length.

The difference in skin color between lightly and darkly pigmented individuals is due not to the number (quantity) of melanocytes in their skin, but to the melanocytes' level of activity (quantity and relative amounts of eumelanin and pheomelanin). This process is under hormonal control, including the MSH and ACTH peptides that are produced from the precursor proopiomelanocortin.

Albinos lack an enzyme called tyrosinase^{[dubious – discuss]}. Tyrosinase is required for melanocytes to produce melanin from the amino acid tyrosine.

Stimulations

Main article: Melanocortin

Numerous stimuli are able to alter melanogenesis, or the production of melanin by cultured melanocytes, although the method by which it works is not fully understood. Melanocortins have been discussed to have effect on appetite and sexual activity in mice.^[8] Vitamin D metabolites, retinoids, melanocyte-stimulating hormone, forskolin, cholera toxin, isobutylmethylxanthine, diacylglycerol analogues, and UV irradiation all trigger melanogenesis and, in turn, pigmentation.^[9] The production of melanin is also initiated by ACTH (an adrenocorticotropic hormone).^{[citation needed]}

Once made, melanin is moved along arm-like structures called dendrites in a special container called a melanosome, which is shipped to the keratinocytes. Melanosomes are vesicles or packages of the chemical inside a plasma membrane. The melanin is in organelles called melanosomes, which are organized as a cap protecting the nucleus of the keratinocyte.

When ultraviolet rays penetrate the skin and damage DNA, thymidine dinucleotide (pTpT) fragments from damaged DNA will trigger melanogenesis^[10] and cause the melanocyte to produce melanosomes, which are then transferred by dendrite to the top layer of keratinocytes.

References

^ Barden H and Levine S (1983). "Histochemical observations on rodent brain melanin". Brain Research Bulletin 10 (6): 847–851. doi:10.1016/0361-9230(83)90218-6. PMID 6616275.
^ Markert CL and Silvers WK (1956). "The effects of genotype and cell environment on melanoblast differentiation in the house mouse". Genetics 41 (3): 429–450. PMC 1209793. PMID 17247639. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1209793/.
^ Mintz B (1971). "Clonal basis of mammalian differentiation". Symposia of the Society for Experimental Biology 25: 345–370. PMID 4940552.
^ Nichols SE and Reams WM (1969). "The occurrence and morphogenesis of melanocytes in the connective tissues of the PET/MCV mouse strain". Journal of Embryology and Experimental Morphology 8: 24–32. PMID 14426921.
^ Theriault LL and Hurley LS (1970). "Ultrastructure of developing melanosomes in C57 black and pallid mice". Developmental Biology 23 (2): 261–275. doi:10.1016/0012-1606(70)90098-9. PMID 5476812.
^ Agar N and Young AR (2005). "Melanogenesis: a photoprotective response to DNA damage?". Mutation Research 571 (1–2): 121–32. doi:10.1016/j.mrfmmm.2004.11.016. PMID 15748643.
^ Parrish JA, Jaenicke KF and Anderson RR (1982). "Erythema And Melanogenesis Action Spectra Of Normal Human Skin". Photochemistry and Photobiology 36 (2): 187–191. doi:10.1111/j.1751-1097.1982.tb04362.x. PMID 7122713.
^ Thompson C and Berger A (2000). "Agent provocateur pursues happiness". BMJ 321 (7252): 12. doi:10.1136/bmj.321.7252.12. PMC 1127681. PMID 10875824. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1127681/.
^ Roméro-Graillet C, Aberdam E, Biagoli N, Massabni W, Ortonne JP and Ballotti R (1996). "Ultraviolet B radiation acts through the nitric oxide and cGMP signal transduction pathway to stimulate melanogenesis in human melanocytes". Journal of Biological Chemistry 271 (45): 28052–6. doi:10.1074/jbc.271.45.28052. PMID 8910416.
^ Eller MS, Maeda T, Magnoni C, Atwal D and Gilchrest BA (1997). "Enhancement of DNA repair in human skin cells by thymidine dinucleotides: evidence for a p53-mediated mammalian SOS response". Proceedings of the National Academy of Sciences of the United States of America 94 (23): 12627–32. doi:10.1073/pnas.94.23.12627. PMC 25061. PMID 9356500. //www.ncbi.nlm.nih.gov/pmc/articles/PMC25061/.

External links

Melanocyte at eMedicine Dictionary
BU Histology Learning System: 07903loa - "Eye: fovea, RPE"
BU Histology Learning System: 08103loa - "Integument: pigmented skin"

UpToDate Contents

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1. 黒色腫（メラノーマ）の分子生物学 the molecular biology of melanoma
2. 後天性色素性母斑（ほくろ） acquired melanocytic nevi moles
3. 皮膚の良性病変の概要 overview of benign lesions of the skin
4. 尋常性白斑 vitiligo
5. 光による老化 photoaging

English Journal

Hordenine, a single compound produced during barley germination, inhibits melanogenesis in human melanocytes.

Kim SC, Lee JH, Kim MH, Lee JA, Kim YB, Jung E, Kim YS, Lee J, Park D.SourceBiospectrum Life Science Institute, Eines Platz 11th FL, #442-13 Sangdaewon Dong, Seongnam City, 462-807 Gyunggi Do, Republic of Korea.
Food chemistry.Food Chem.2013 Nov 1;141(1):174-81. doi: 10.1016/j.foodchem.2013.03.017. Epub 2013 Mar 14.
Melanin plays an important role protecting skin against ultraviolet light injury. However, increased production and accumulation of melanin results in a large number of skin disorders. Here, we identified hordenine as an active compound from germinated barley (Hordeum vulgare L.) and investigated th
PMID 23768344

Characterization of the trunk neural crest in the bamboo shark, Chiloscyllium punctatum.

Juarez M, Reyes M, Coleman T, Rotenstein L, Sao S, Martinez D, Jones M, Mackelprang R, De Bellard ME.SourceBiology Department, California State University Northridge, Northridge, California, 91330.
The Journal of comparative neurology.J Comp Neurol.2013 Oct 1;521(14):3303-20. doi: 10.1002/cne.23351.
The neural crest is a population of mesenchymal cells that after migrating from the neural tube gives rise to structure and cell types: the jaw, part of the peripheral ganglia, and melanocytes. Although much is known about neural crest development in jawed vertebrates, a clear picture of trunk neura
PMID 23640803

Identification of genes influencing formation of the Type III Brush Hair in Yangtze River Delta white goats by differential display of mRNA.

Li Y, Li W, Zhang J, Ji D, Zhang G, Yang B.SourceCollege of Animal Science and Technology, Yangzhou University, Key Laboratory for Animal Genetic, Breeding, Reproduction and Molecular Design of Jiangsu Province, Yangzhou, Jiangsu 225009, PR China. Electronic address: liyj@yzu.edu.cn.
Gene.Gene.2013 Sep 10;526(2):205-9. doi: 10.1016/j.gene.2013.05.030. Epub 2013 Jun 2.
Yangtze River Delta white goat is an exclusive indigenous Chinese goat breeds that can produce Brush Hair specialized in making valuable writing brush. The high-grade (Type III) Brush Hair is conical coarse hair but with a tip, which only grows in the cervical carina and back regions of Yangtze Rive
PMID 23735839

Japanese Journal

メラノソームの微小管逆行輸送機構 : 白髪予防の新たな分子標的 (特集ヘアカラー製品のための技術開発と毛髪研究)

大林典彦,福田光則
Fragrance journal 42(3), 30-35, 2014-03
NAID 40020022629

The Mouse Brown (b/Tyrp1[b]) Allele Does Not Affect Pheomelanin Synthesis in Mice

Hirobe Tomohisa,Ito Shosuke,Wakamatsu Kazumasa [他]
Zoological science 31(2), 53-63, 2014-02
NAID 40019989060

Analysis of the Effects of Hydroquinone and Arbutin on the Differentiation of Melanocytes

Inoue Yu,Hasegawa Seiji,Yamada Takaaki [他]
Biological & pharmaceutical bulletin 36(11), 1722-1730, 2013-11
NAID 40019842836

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★リンクテーブル★

リンク元	「メラノサイト」「メラニン形成細胞」「melanocytic」
拡張検索	「melanocyte-stimulating hormone」「gamma-melanocyte-stimulating hormone」「α-melanocyte stimulating hormone」